Constant current regulator with moving coil transformer



April 22, 1969 I J,M CEMO'N 3,440,519

CONSTANT CURRENT REGULATOR WITH MOVING COIL TRANSFORMER Filed NOV. 16.1966 United States Patent 3,440,519 CONSTANT CURRENT REGULATOR WITHMOVING COIL TRANSFORMER Herbert J. Macemon, Hendersonville, N.C.,assignor to General Electric Company, a corporation of New York FiledNov. 16, 1966, Ser. No. 594,911 Int. Cl. Gf l /16 US. Cl. 323-6 5 ClaimsABSTRACT OF THE DISCLOSURE A constant current regulator to controllighting systems or heating devices. The regulator has a moving coiltransformer wherein the primary winding or a main secondary windingconnected to the load are movable relative to each other. An auxiliarysecondary winding has a controlled rectifier switching circuit connectedacross it to control the current in the main secondary winding.

The present invention relates to a constant current regulator, andparticularly a constant current regulator of moving coil transformertype.

It is an object of the invention to provide a constant current regulatorof the above type which provides for stepless control of the constantcurrent produced thereby.

Another object of the invention is to provide a constant currentregulator of the above type which is compact and lightweight, isreliable in operation, has low losses, and which automatically limitsshort circuit current.

It is a particular object of the invention to provide a constant currentregulator of the above type which provides for control of the outputcurrent by controlling a circulating current in an auxiliary winding ofthe moving coil transformer.

Other objects and advantages will become apparent from the followingdescription and the appended claims.

With the above objects in view, the present invention relates to aconstant current regulator comprising, in combination, a moving coilconstant current transformer having main primary and secondary windings,at least one of the windings being movable relative to the other formaintaining a constant current in the secondary winding, the mainprimary winding having terminals connected thereto for connection to asource of alternating current, load means connected to the mainsecondary winding, control circuit means associated with the mainsecondary winding for varying the level of current supplied to the loadmeans comprising an auxiliary secondary winding adjacent the mainsecondary winding, and means connected across the auxiliary secondarywinding for controlling the current flow therein and thereby in the mainsecondary winding, whereby the current to the load means may becontrolled by the control circuit means.

In the preferred embodiment of the invention, the means connected acrossthe auxiliary secondary winding is a phase control means comprisingcontrolled rectifier means.

The invention will be better understood from the following descriptiontaking in conjunction with the accompanying drawing, in which:

The single figure is a circuit diagram of an embodiment of the improvedconstant current regulator of the invention.

Referring now to the drawing, there is shown a circuit arrangementenergizing at a constant current a load 1, such as an illuminatingmeans. The illuminating means may be constituted by one or more lampssuch as incandescent, gaseous discharge or fluorescent-type lamps. Thecircuit includes a movable coil constant current transformer 3comprising a main primary winding 3a connected to terminals 2 of asource of alternating current and a main secondary winding 3b acrosswhich load 1 is connected. In such a movable coil transformer 3, eitherprimary coil 3a or secondary coil 3b may be made movable on the corerelative to the other, or both coils may be movable with respect to eachother and the core. In such a device, the magnitude of the outputcurrent is controlled by the effective weight of the moving coilstructure. In operation, this weight is exactly balanced by therepulsion forces produced by the currents flowing in the primary andsecondary coils. These repulsion forces are proportional to the squareof the secondary ampereturns. Variations in either input voltage oroutput load result in the moving coil seeking a new position relative tothe other coil so that again the Weight of the moving coil assembly andthe repulsion forces between coils are balanced, resulting inmaintaining a constant output current over the designed range of travelof the moving coil. With a constant output current and a fixed number ofturns in the secondary coil, the total ampere-turns in the secondary isa constant. In the regulator circuit employed in the invention, acontrol device is incorporated for varying in stepless fashion the levelof the constant output current which would otherwise be fixed. Inaccordance with the principles of the invention, such control isachieved by providing a control circuit comprising an auxiliarysecondary winding on transformer 3 and a means for controlling the flowof current in the latter winding. When current flows in the auxiliarywinding, the ampere-turns in the auxiliary winding directly subtractfrom the total constant ampere-turns available to the main secondarycoil (output) circuit, and hence the magnitude of the output current isreduced to a lower constant level. Preferably, current flow in theauxiliary winding should be controlled without introducing significantadditional losses. In the embodiment shown in the drawing, the controldevice comprises auxiliary second ary winding 4, adjacent the mainsecondary winding 3b and in fixed spatial relation thereto. Connectedacross auxiliary secondary winding 4 is a controlled rectifier switchingcircuit 5 which serves to provide a phase controlled current of desiredamount in winding 4 to thereby vary the ampere-turns of main secondarycoil 3b, thus resulting in the desired adjustment of the constantcurrent supplied to load 1. Controlled rectifier circuit 5 includes aparalleled pair of oppositely poled controlled rectifiers 7 and 8, whichare typically silicon controlled rectifiers (SCRs) having controlled(gate) electrodes 7 and 8 by means of which the SCRs are renderedconductive for unidirectional flow of current when a signal pulse isapplied to the respective control (gate) electrodes.

Control electrodes 7' and 8' are connected respectively to secondarywindings 9a, 9b of coupling transformer 9. Transformer 9 serves toisolate the controlled rectifier circuit 5 from the trigger pulsegenerating circuit described below. The signal generating or actuatingcircuit 23 comprises a variable resistance 10 in series with a chargingcapacitor 11 connected across auxiliary winding4.

A discharge loop in actuating circuit 23 for discharging capacitor 11includes transformer primary 9c and a voltage sensitive device 12,typically a neon-glow lamp, which is a bi-laterally conducting diode,and is also referred to herein as a voltage sensitive symmetrical switchmeans, which becomes conductive only upon the application of apredetermined voltage thereto. Other symmetrical switch devices whichcould alternatively be used are a diac, a symmetrical Shockley device,or the like. Voltage sensitive switch 12 is connected in parallel withcharging capacitor 11 but is eifectively connected in series dischargerelation therewith and with transformer primary 9c as shown. Anauxiliary discharge capacitor 13 is also preferably arranged inserieswith these components of the discharge loop' as shown, so as to providea residual charge additive to the voltage appearing across capacitor 11on each half cycle, as more fully explained in the patent to Nuckolls3,249,807.

In-the above described circuit arrangement, on each half cycle of thealternating current input derived from auxiliary secondary winding 4,one of the controlled rectifiers 7 and 8 will have a positive anode andthe other a positive cathode. Therefore, a control signal applied tocontrol electrode 7' and 8' will place only one of the controlledrectifiers in a conduction mode on each half cycle. A delay in the pointin the alternating current input cycle at which the control signalimpulse is applied to render the rectifier conductive is known as phasecontrol. The characteristics and function of SCR switching circuit andits actuating circuit 23 are more fully described in the aforementionedNuckolls patent, the disclosure of which is incorporated herein byreference.

As there described, voltage sensitive switch 12 becomes conductive as aresult of the voltage buildup on capacitor 11, capacitor 11 partiallydischarges and a signal pulse is applied to the transformer primary 9cwhich induces a current pulse of a particular duration and at aparticular time in the half cycle. The controlled rectifier 7 or 8 whichhas an anode positive with respect to cathode will then be triggered toconduction by the pulse current applied to control electrode 7', 8' andthe voltage which has built up across the rectifier falls substantiallyto zero. The controlled rectifier 7 or 8 then permits current to flow,consequently circulating current through auxiliary secondary winding 4for the remainder of that half cycle. On the next half cycle as theanode voltage becomes negative, the controlled rectifier 7 or 8 whichwas conductive becomes nonconductive and no current is transmittedthrough winding 4 until the signal generating circuit fires the othercontrolled rectifier. The time in the half cycle at which the rectifieris gated is adjustable by the level of resistance 10.

For the purpose of protecting rectifier circuit 5 from transientvoltages, a thyrector 16, or double Zener diode device, may be connectedin parallel with the rectifiers, as shown.

By suitable adjustment of variable resistance 10, which may be employedas a manually operated control means for the lighting circuit or otherload, the current circulating in auxiliary secondary coil 4 may bevaried by means of the described SCR phase control device. As indicatedpreviously, the change in current thus produced in coil 4 results invariation of the ampere-turns in that coil, which subtract from thetotal ampere-turns in main secondary coil 3b, thus effecting a change inthe load current in the latter circuit.

While a phase control arrangement as described above is preferred inaccordance with the invention, other means may be substituted for SCRcircuit 5 and actuating circuit 23 for short circuiting or controllingcurrent flow in auxiliary winding 4. For example, a variable impedancedevice such as a variable resistor, a variable capacitor, or a variableinductance may simply be connected across auxiliary secondary winding 4to control the current circulating therein. r

While the described constant current regulator device has been disclosedas applicable for use in the control of lighting systems, it will beunderstood that it may also be found useful for control of other typesof apparatus which is designed to operate at varying levels of constantcurrent, as for example electric ovens and other heating devices.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A current regulator device comprising, in combination, a moving coilconstant current transformer having main primary and secondary windings,and having terminals connected to said main primary winding forconnection to a source of alternating current, load means connected tosaid main secondary winding for energization thereby at a substantiallyconstant current, and control circuit means associated with said mainsecondary winding for varying the level of constant current supplied tosaid load means comprising an auxiliary secondary winding adjacent tosaid main secondary winding.

2. A device as defined in claim 1, said control circuit means includingphase control means connected to said auxiliary secondary winding forcontrolling the current in the latter winding.

3. A device as defined in claim 2, said phase control means comprisingbi-directional conducting controlled rectifier means connected acrosssaid auxiliary secondary winding and being normally non-conductive toblock current flow through said auxiliary secondary winding and havingelectrode control means to render it conductive in either directiondepending on the polarity of the alternating current supply, and meansfor applying a control signal to said electrode control means includinga capacitance and a resistance connected together in series across saidauxiliary secondary winding, and voltage sensitive switch means andtransformer means connected across said capacitance in series dischargerelation therewith.

4. A device as defined in claim 3, wherein said resistance is a variableresistor.

5. A device as defined in claim 1, said control circuit means comprisingvariable impedance means connected to said auxiliary secondary windingfor controlling the current in the latter winding and thereby elfectingcontrol of the output current.

References Cited UNITED STATES PATENTS Trigger Circuits, third edition,1964, p. 139.

JOHN F. COUCH, Primary Examiner.

A. D. PELLINEN, Assistant Examiner.

US. Cl. X.R.

